<!DOCTYPE html>
<html>
<head>
    <style type="text/css">
        .main{
            position:absolute;
            top:50%;
            left:50%;
            -moz-transform: translate(-50%,-50%);
            -o-transform: translate(-50%,-50%);
            -ms-transform: translate(-50%,-50%);
            transform: translate(-50%,-50%);
            width:400px;
            min-height:200px;
            background-color: #ccc;
            overflow: hidden;
        }
        .left-top{
            position:absolute;
            top:-50px;
            left:-50px;
            width:100px;
            height:100px;
            background-color: #fc0;
            -webkit-border-radius:50px;
            -moz-border-radius:50px;
            border-radius:50px;
        }
        .right-bottom{
            position:absolute;
            bottom:-50px;
            right:-50px;
            width:100px;
            height:100px;
            background-color: #fc0;
            -webkit-border-radius:50px;
            -moz-border-radius:50px;
            border-radius:50px;
        }
    </style>
</head>
<body>
<div class="main">
    <div class="left-top">
    </div>
    <div class="right-bottom">
    </div>
</div>
</body>
</html>